1. Field of the Invention
The present invention relates to signal transmission in a printed circuit board (PCB).
2. Description of the Related Art
Generally, high-speed transmission of a plurality of signals requires that a difference in transmission time between the signals (referred to as a skew hereinafter) be decreased as far as possible. It is necessary to greatly reduce a skew between the differential pairs of differential signals in order to achieve high-speed digital signal transmission on the LVDS (low voltage differential signaling) system, for instance.
There has been on the one hand some conventional electronics in which a plurality of specific signals whose delay amount should be matched are assigned to connector terminals of the same connector type, respectively to thereby reduce the skew between those signals to a minimum. Moreover, there has been on the other hand some conventional electronics using the trace pattern of signal lines, where the signal line of which length from a serial transfer controller to a connector terminal is longest is traced straight and signal line other than the above signal line is provided with a bent portion such that the length thereof comes to be the same as that of the signal line. For instance, JP, 2001-022486, A (pp. 4, FIG. 1) discloses an electronics in which the skew is reduced to a minimum by adopting these techniques.
Incidentally, a technique for transmitting a plurality of signals in a PCB has been developed, in which a plurality of signal lines are traced in the internal layers of the board. The terminals of the internal-layer signal line are connected with another device via through holes formed in the PCB. Such a technique entails a demand for reduction of the skew while the influence due to a reflection characteristic of the through holes is decreased to a minimum.